The 3GPP that is a standardization organization of W-CDMA (Wideband Code Division Multiple Access) has defied a communication system that is a successor to W-CDMA and HSDPA (High Speed Downlink Packet Access) i.e. Long Term Evolution (LTE), and has adopted OFDMA (Orthogonal Frequency Division Multiple Access) in downlink, and SC-FDMA (Single-Carrier Frequency Division Multiple Access) in uplink. Currently, the 3GPP has studied a system successor to LTE (LTE-Advanced or Release 10).
The LTE system is a system in which a plurality of mobile stations UEs shares one, or two physical channels or more in both uplink and downlink to perform communications. The channels shared by a plurality of mobile stations UEs are generally called the shared channels, and in LTE, are the PDSCH (Physical Downlink Shared Channel) in downlink and the PUSCH (Physical Uplink Shared Channel) in uplink.
In the LTE system, a base station eNB transmits a downlink control channel (PDCCH: Physical Downlink Control Channel) and PDSCH to a mobile station UE on a subframe-by-subframe basis. The mobile station UE demodulates the PDCCH to acquire a control signal for PDSCH demodulation, and based on the acquired control signal, demodulates the PDSCH. Then, the mobile station UE transmits an ACK/NACK signal indicative of the presence or absence of a packet error in decoding the PDSCH to the base station eNB on an uplink control channel (PUCCH: Physical Uplink Control CHannel).